Composite floor system

ABSTRACT

The present invention concerns a framing system for a composite concrete floor, the framing system comprising horizontally extending primary framing members supporting secondary framing members across the primary framing members. Each of the secondary framing members has two opposite ends provided with a shear shoe fixed to the primary framing members by means of a structural joint sufficient to provide a shear connection between the concrete floor and the primary framing members. Thanks to these shear shoes, the framing system of the invention has an increased resistance to horizontal shear forces as compared to prior art concrete floor systems.

FIELD OF THE INVENTION

[0001] The present invention relates generally to composite steel andconcrete floor systems of the type including reinforced concrete slabssupported by secondary framing members such as steel joists, which inturn are spanned across primary framing members, such as hot rolledsteel, beams, girders, or trusses. More particularly, it concerns acomposite concrete floor system comprising secondary framing membersprovided with shear shoes at their ends. These shear shoes are adaptedto provide to the whole system an increased resistance to horizontalshear forces.

BACKGROUND OF THE INVENTION

[0002] In composite floor structures, it is known to couple the concreteand steel components to provide composite action, thereby reducing theamount of material in the floor system for a given required strength. Byusing the concrete slab as the top chord of a composite beam, asignificant reduction in the amount of steel in the floor system isachieved. Such floor systems are known in the art. One well known systemof secondary members is sold as the Hambro™ structural system. Thissystem is disclosed in U.S. Pat. No. 5,544,464.

[0003] In residential buildings, it is common to arrange the structureto span open web joists between load bearing walls, and no primaryframing members are required to support the joists. In largerstructures, the joists are generally supported by primary framingmembers in the form of steel beams or trusses. This is particularly thecase for steel framed buildings which are erected as steel columnsconnected by and supporting primary steel framing members. Secondarysteel framing members, for example in the form of open web steel joists,are spanned across the primary members, and loads are transferred by theprimary members to the columns, and to the foundations of the building.

[0004] These structures must resist to many forces, both horizontal andvertical and, as such, their design is complex and require theapplication of much scientific skill and knowledge. One of the forcesencountered in these structures is known as horizontal shear. This is ahorizontal force which occurs along the longitudinal top of primary andsecondary frame members. The Hambro™ joist described in U.S. Pat. No.5,544,464 is provided with a unique S-shaped top chord which, whenembedded in the concrete slab, forms a shear connector to preventslippage from occurring between the concrete slab and the joist, due tohorizontal shear along the joist.

[0005] Various forms of shear connectors have been developed for theprimary steel framing members, the most common being the headed shearstud, or Nelson™ stud, an elongated vertical device, which has anenlarged head, much like an oversized nail. This stud is welded to thesteel beam after the beam has been connected to the structure duringerection. This stud provides the necessary shear capacity between theembedded stud and the concrete slab, thereby providing a composite steelbeam or girder. The stud is intended to be imbedded in the concrete,thereby transferring horizontal shear forces from the slab to the beam.

[0006] The most cost effective way to provide shear studs is to installthem in the shop. However, one drawback with such shear connector isthat these studs constitute a tripping hazard for steel workers who haveto walk on these beams during erection of the frame. The seriousness ofthe problem is highlighted by the fact that for more than 25 years, theInternational Ironworker Agreement has rejected the use of such studs onsteel beams. These rules were adopted by safety committees as they wereformed in Canada and the USA, such as OSHA. In order to overcome thatproblem, the studs are generally welded to the primary steel members onthe site of construction. In such a case, the secondary framing members(also referred to as steel joists) are first installed on the primarysteel member, then the steel deck is installed, and then the studs arewelded through the metal decking on the steel top chord. Theinstallation of the shear studs on the site of construction createsquality problems due to the very nature of the welding process. Also,since the installation of these studs is weather dependant, anotherdrawback encountered with such “on site” installation comes from thefact that it is often very difficult to schedule the skilled labourrequired and to manage such schedule so as to follow the fast pace ofstructural steel erection program.

[0007] Other examples of concrete floor systems are given in U.S. Pat.Nos. 4,729,201; 6,061,992; U.S. 2003/0024205; U.S. 2003/0084629; U.S.Pat. Nos. 4,454,695; 4,700,519 and 4,592,184.

[0008] Thus there is a need for a new form of shear connector for theprimary framing members which leaves the top flange essentially flat forwalking purposes, and avoids the installation and scheduling problems.

SUMMARY OF THE INVENTION

[0009] In accordance with the present invention, that object is achievedwith a framing system for a composite concrete floor of the typecomprising horizontally extending primary framing members supportingsecondary framing members spanning across the primary framing members,the primary and secondary framing members being made of a metallicstructural material. Each of the secondary members has two opposite endsprovided with a shear shoe that is fixed to the primary members by meansof a structural joint sufficient to provide a shear connection betweenthe concrete floor and the primary framing members.

[0010] The metallic structural material is preferably steel or any othermetallic structural material known in the art. The present invention isthus not limited to steel framing members. Therefore, whenever referenceis made throughout the present description to steel beams, steel joists,one should understand beams, joists or framing members made of ametallic structural material.

[0011] The shear shoes of the secondary members preferably consist of aniron angle having one horizontally extending face fixed by means of thestructural joint to a horizontal face of a respective one of the primaryframing members, and one vertically extending face fixed to saidsecondary framing member.

[0012] Also preferably, the structural joint is selected from the groupconsisting of a weld joint and a bolt joint.

[0013] As can be appreciated, the present invention forms a mechanicalshear connection for primary framing members which does not create atripping hazard during erection and prior to the composite stage, whenthe concrete floor slab has been formed and is cured, which shearconnection effectively transfers horizontal shear forces to the primaryframe members.

[0014] Thus, the present invention provides, among other things, all theadvantages of composite steel/concrete floor slab construction, with theadded advantage of an efficient horizontal shear connection to primarysteel floor members, allowing a continuous poured slab for an entirefloor of a building to be formed with no tripping hazards for ironworkers, due to shear connectors. Such a structure is also designed bystructural engineers to meet all other loads encountered in usualbuilding construction.

[0015] In a further aspect, the present invention provides a method ofassembling the framing members to concrete. The method comprises thesteps of:

[0016] providing primary and secondary framing members made of ametallic structural material, each of the secondary framing membershaving two opposite ends provided with a shoe;

[0017] placing the primary framing members in parallel relation;

[0018] placing the secondary framing members across the primary memberswith the shoes bearing on the primary framing members; and

[0019] fixing the shoes to the primary framing members with a structuraljoint sufficient to provide a shear connection for said primary members.

[0020] Preferably, the step of fixing consists of welding the shoes tothe primary framing members. Also preferably, the secondary framingmembers have a continuous shear connector.

[0021] More preferably, the shear connector is a continuous top chordadapted to be embedded in the concrete floor.

[0022] The present invention further provides a new end shoe concept ora novel end shoe for connecting the joist to the beam. The inventionalso provides a novel joist with an end shoe which serves as the shearconnector for the beam to which it is attached.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] These and other objects and advantages of the invention willbecome apparent upon reading the detailed description and upon referringto the drawings in which:

[0024]FIG. 1 is an overhead perspective view of a composite floor inaccordance with the present invention, with the concrete slab partiallyremoved to show the steel frame members;

[0025]FIG. 2 is a cross-sectional view through a floor system inaccordance with a first preferred embodiment of the invention, thecross-sectional view being perpendicular to a primary framing member;

[0026]FIG. 3 is a cross-sectional view at right angle to the section ofFIG. 2 along line 3-3 and showing the shear force applied on a shearshoe;

[0027]FIG. 4 is a cross-sectional view of the mounting of secondaryframe members in the form of open web steel joists on a primary steelbeam member of the floor system of FIG. 2;

[0028]FIG. 5 is a cross-sectional view of a primary frame trusssupporting open web steel joists;

[0029]FIG. 6 is an enlarged perspective view of the frame members ofFIG. 5;

[0030]FIG. 7 is an end elevation view of a frame truss or joist girderfor use in the floor system of the invention;

[0031]FIG. 8 is an end elevation view of the joist truss supporting twojoists of the present invention;

[0032]FIG. 9 is a plan view of the joist truss supporting a plurality ofopen web joists of the invention;

[0033]FIGS. 10 and 11 are side elevation views of joist truss girdersbefore and after the concrete has been poured;

[0034]FIG. 12 is a plan view of a primary framing member supportingstaggered secondary framing members, with end shoes welded to theprimary framing member;

[0035]FIG. 13 is a cross-sectional view through a floor system inaccordance with a second preferred embodiment of the invention, thecross section being perpendicular to a primary framing member;

[0036]FIG. 14 is a cross-sectional view at right angle to the section ofFIG. 13 along line 14-14, and showing the shear force applied on a shearshoe; and

[0037]FIG. 15 is a cross-sectional view of the mounting of secondaryframing members in the form of open web steel joists on a primary steelbeam member of the floor system shown in FIG. 13.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

[0038] In the following description, similar features in the drawingshave been given similar reference numerals and in order to lighten thefigures, some elements are not referred to in some figures if they werealready identified in a precedent figure.

[0039] Referring to FIG. 1, there is shown, in perspective, an overheadview of a composite floor system of the invention. A primary framingmember 11, which is shown here as a steel truss or girder, supports aplurality of secondary framing members 12 formed as open web steeljoists which span perpendicularly between adjacent primary framingmembers (not shown). Each joist 12 is provided with an end shoe 13 oneach end of the joist for attachment to the primary framing member 11.FIG. 6 shows this in greater detail, as explained below. Preferably, theprimary framing member 12 used is a Hambro™ joist provided with anS-shaped top chord which forms a shear connector between the primaryframing member 12 and the concrete slab 14. A concrete slab 14 withreinforcing mesh 15 is poured onto form-work (not shown for simplicity)and embeds the top chord 16 of the joists 12 and the top chord 17 of theprimary framing members 11. The end shoes 13 of the joists 12 are fixedto the primary framing member 11 by means of a structural joint 15sufficient to provide a shear connection between the concrete floor 14and the primary framing members 12.

[0040] The shear shoe thus acts as a shear connector able to transferthe horizontal loading from the slab to the primary framing member bythe end shoe structurally fixed to the primary framing member 11. Thestructural joint 15 is preferably a weld joint between the shear shoe 13and the primary framing member 11, the weld having a length sufficientlylong so as to provide such structural joint. Although not simple, thedetermination of shear capacity between two components is of commonknowledge for a person in the art. Hence, such person, having knowledgeof the forces applied on the floor, the length and height of the primaryand secondary framing members used for the floor system, knows how tocalculate the shear necessary to develop the composite action betweensecondary and primary framing members and the right spacing between theconnectors. As for example, in one preferred embodiment, an end shoeHambro D500™ with a concrete slab of 2¾ inches reinforced by a wire mesh6×6 {fraction (6/6)} fixed to the primary framing members by a weld ofat least 2 inches provided on each side of the shoe can provide acapacity of 30.2 Kips per shoe. The total capacity provided will be thenumber of shoes installed on the primary framing member by 30.2 Kips pershoe.

[0041]FIG. 2 shows a primary framing member in the form of a steel beam11′ supporting a joist 12 fitted with an end shoe 13 welded to the beam11′. This weld is shown in greater detail in FIG. 6 below. The end shoe13 is also referred to hereinafter as a “shear shoe”.

[0042] In FIG. 3, the same beam 11′ as shown in FIG. 2 is shown inelevation, with the arrow 20 indicating the direction of the horizontalshear force. The combination of the joist 12, the end shoe 13 and thewelding of the end shoe 12 to the primary member 11 creates a shearconnector to resist the horizontal shear forces between the slab 14 andthe primary framing member 11 or 11′.

[0043] The advantages of this new shear connector are many. First, thereis the utilization of the joist end shoe 13 designed and analyzed toprovide a bond included in each secondary framing member 11. The shearshoe 13 performs a double function of supporting the gravity load on thejoist and also provides a mechanical shear connector able to transferthe bond between the slab 14 and the primary framing member 11. Thistype of shear connection also avoids the tripping hazard on the site,according to labour union rules, and increases erection speed of thesteel building frame.

[0044] The present invention features the use of special ends or shearshoes 13 which act as shear connectors to the flange of a steel beam orthe top chord of a truss. The shoe 13 is also a gravity shoe for thesecondary steel framing member 12 and shear connector tested anddesigned according to the capacity required for the composite trusses.The welding between the top chord of the truss or beam forming theprimary framing member 11 and the shoe 13 is designed according to thecapacity required. The open web joist of the secondary framing members12 can be used in a deck-slab system such as Hambro MD2000™ system orwith a removable plywood system such as Hambro D500™.

[0045] Depending on the loading and span of the primary framing member11, single shoe connectors 13 can be used, or groups of connectors. Thetotal capacity in bond will be the total capacity of all shoe connectorsand other connectors.

[0046]FIG. 4 illustrates a pair of open web joist secondary members 12,which may be aligned or staggered, mounted on a primary framing member11. Each joist 12 is provided with a dual purpose shear shoe 13 which iswelded to the joist 12 in manufacture, and delivered to the job-site,ready for installation. Each shoe 13 is then welded or bolted to the topflange of the regular beam primary framing member 11. Similarly, FIG. 5illustrates a pair of joists 12 with shear shoes 13 mounted on a primarytruss framing member 11. As before the shoes are welded to the topflanges of the truss 11. In both of these cases, horizontal shearbetween the primary framing member and the slab is transferred from theslab to the primary framing member by the shear shoes 13.

[0047]FIG. 6 is a perspective view from above of the connection of thesecondary open web joists 12 and the primary truss framing member 11.Welds 21 are provided on both sides of shear shoes 13 to fix the shoes13 to the top flanges of the truss 11.

[0048]FIG. 7 is a vertical section of a primary steel truss framingmember 11 consisting of a bottom chord formed of angles 30 weldedback-to-back between web members 32 which in turn are welded to a gussetplate 32 which in turn is welded to a back-to-back top chord angle 33.The vertical legs of the angles 33 are slotted at intervals, the slotsbeing staggered, and rod segments 34 are welded to the vertical legs ofthe angles 33.

[0049] This novel truss construction provides a strong, light primaryframing member with maximum openings in the web through which buildingservices such as heating, plumbing, electricity, and communicationservices can be located. FIG. 8 shows the connection of primary andsecondary framing members using the truss of FIG. 7, integrating thewhole frame structure to resist horizontal shear forces, and support thegravity load of the floor system.

[0050]FIG. 9 is a plan view of a portion of a floor frame system 10including a primary truss 11, and secondary joists 12 with end shoes 13,in which the joists are aligned rather than staggered.

[0051]FIGS. 10 and 11 show alternate truss configurations depending onbuilding requirements, FIG. 10 being the standard configuration and FIG.11 being a configuration for maximum size openings in the truss foraccommodating large ducts.

[0052]FIG. 12 is a plan view of a primary steel beam framing member 11supporting staggered secondary open web joist members 12 with shearshoes 13 welded to the member 11. Such staggering of the secondarymembers is required when shear connectors are required at intervals lessthan the normal joist spacing.

[0053] Referring to FIG. 13, a concrete floor system according to asecond preferred embodiment of the invention is illustrated. As for thefirst preferred embodiment shown in FIG. 2, the floor system comprises aprimary framing member in the form of a steel beam 11′ supporting ajoist 12 fitted with an end shoe 13 welded to the beam 11′, the wholestructure supporting a concrete floor 14. The difference between thefirst preferred embodiment shown in FIGS. 2 to 12 and the secondembodiment resides mainly in the fact that, in the first embodiment, theshear shoes 13 are embedded in the concrete, whereas the shear shoes 13in the second embodiment are not, the concrete being poured on top ofthe secondary framing members 12.

[0054] In FIG. 14, the same beam as shown in FIG. 13 is shown inelevation, with the arrow 20 indicating the direction of the horizontalshear force. The combination of the primary framing member 12, the endshoe 13 and the welding of the end shoe 13 to the primary framing member11 creates a shear connector to resist the horizontal shear forcesbetween the slab 14 and the primary framing member 11 or 11′.

[0055] Although preferred embodiments of the present invention have beendescribed in detail herein and illustrated in the accompanying drawings,it is to be understood that the invention is not limited to theseprecise embodiments and that various changes and modifications may beeffected therein without departing from the scope or spirit of thepresent invention.

What is claimed is:
 1. A framing system for a composite concrete floor,the framing system comprising horizontally extending primary framingmembers supporting secondary framing members across the primary framingmembers, said primary and secondary framing members being made of ametallic structural material, each of said secondary framing membershaving two opposite ends provided with a shear shoe, said shear shoebeing fixed to said primary framing members by means of a structuraljoint sufficient to provide a shear connection between said concretefloor and said primary framing members.
 2. A framing system as definedin claim 1, wherein said shear shoes of each secondary framing membercomprise an iron angle having: one horizontally extending face fixed bymeans of said structural joint to a horizontal face of a respective oneof said primary framing members, and one vertically extending face fixedto said secondary framing members.
 3. A framing system as defined inclaim 2, wherein said structural joint is selected from the groupconsisting of a weld joint and a bolt joint.
 4. A framing system asdefined in claim 3, wherein said structural joint is a weld joint.
 5. Aframing system as defined in claim 1, wherein said secondary framingmembers have continuous shear connection to the concrete floor.
 6. Aframing system as defined in claim 5, wherein said secondary framingmembers have a top chord embedded in the concrete floor, therebyproviding said shear connection to the concrete floor.
 7. A framingsystem as defined in claim 1, wherein said primary framing member is atruss.
 8. A framing system as defined in claim 1, wherein said primaryframing member is a steel beam.
 9. A framing system as defined in claim8, wherein said secondary framing members are open-web steel joint. 10.A framing system as defined in claim 1, wherein said metallic structuralmaterial is steel.
 11. A method of erecting a framing system for acomposite concrete floor comprising the steps of: providing primary andsecondary framing members made of a metallic structural material, eachof said secondary framing members having two opposite ends provided witha shoe; placing said primary framing members in parallel relation;placing said secondary framing members transversally between saidprimary framing members with said shoes bearing on the primary framingmembers; and fixing said shoes to said primary framing members with astructural joint sufficient to provide a shear connection for saidprimary framing members.
 12. A method as defined in claim 11, whereinsaid step of fixing consists of welding said shoes to the primaryframing members.
 13. A method as defined in claim 11, wherein saidsecondary framing members have a continuous shear connector.
 14. Amethod as claimed in claim 13, wherein said shear connector is acontinuous top chord adapted to be embedded in said concrete floor.